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authorMarkos Chandras <mchandras@suse.de>2018-02-19 17:51:42 +0000
committerGerrit Code Review <gerrit@opnfv.org>2018-02-21 08:38:19 +0000
commit930c8e220a1838b080a372c9b5a33600998f64c7 (patch)
treec6b38cadc14353c45124760b2bb54063d8de201e /scripts/docs-build.sh
parentb02bfa0b1e06754d6090aa44dc1894ceeb8ad54f (diff)
Update git submodules
* Update docs/submodules/releng-xci from branch 'master' - xci: Switch VM disk cache to 'unsafe' and use 'iothreads' for I/O According to the docs[1] "writeback: This mode causes the hypervisor to interact with the disk image file or block device with neither O_DSYNC nor O_DIRECT semantics. The host page cache is used and writes are reported to the guest as completed when they are placed in the host page cache. The normal page cache management will handle commitment to the storage device. Additionally, the guest's virtual storage adapter is informed of the writeback cache, so the guest would be expected to send down flush commands as needed to manage data integrity. Analogous to a raid controller with RAM cache." and "writeback: This mode informs the guest of the presence of a write cache, and relies on the guest to send flush commands as needed to maintain data integrity within its disk image. This is a common storage design which is completely accounted for within modern file systems. This mode exposes the guest to data loss in the unlikely case of a host failure, because there is a window of time between the time a write is reported as completed, and that write being committed to the storage device." "unsafe: This mode is similar to writeback caching except for the following: the guest flush commands are ignored, nullifying the data integrity control of these flush commands, and resulting in a higher risk of data loss because of host failure. The name “unsafe” should serve as a warning that there is a much higher potential for data loss because of a host failure than with the other modes. As the guest terminates, the cached data is flushed at that time." It's beneficial to use the host page cache to cache I/O from the guest instead of waiting for data to reach the actual disk device. We do not normally care about data integrity so data loss is not a problem. Moreover, we drop the cache configuration from the flavor files since it's independent of the flavor that's being deployed. [1] https://www.suse.com/documentation/sles-12/singlehtml/book_virt/book_virt.html#cha.cachemodes Change-Id: I118ffdf84b1be672185b3eff60fe5d0b5f1a590d Signed-off-by: Markos Chandras <mchandras@suse.de>
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